What's the most energy efficient way to heat a pool with gas?

We recently bought our home and the pool has a gas heater. Is it more cost effective for us to turn it on high and wait for it to heat when we're planning to swim, or should we leave it on at low during the cooler seasons? We're hoping to install solar heating, but it'll be several more years before we can make that investment, so we'd like to be as responsible and frugal as possible with the gas. Thanks!